Cerebellar and thalamic connector hubs facilitate the involvement of visual and cognitive networks in essential tremor.

INTRODUCTION: Connector hubs are specialized brain regions that connect multiple brain networks and therefore have the potential to affect the functions of multiple systems. This study aims to examine the involvement of connector hub regions in essential tremor. METHODS: We examined whole-brain functional connectivity alterations across multiple brain networks in 27 patients with essential tremor and 27 age- and sex-matched healthy controls to identify affected hub regions using a network metric called functional connectivity overlap ratio estimated from resting-state functional MRI. We also evaluated the relationships of affected hubs with cognitive and tremor scores in all patients and with motor function improvement scores in 15 patients who underwent postoperative follow-up evaluations after focused ultrasound thalamotomy. RESULTS: We have identified affected connector hubs in the cerebellum and thalamus. Specifically, the dentate nucleus in the cerebellum and the dorsomedial thalamus exhibited more extensive connections with the sensorimotor network in patients. Moreover, the connections of the thalamic pulvinar with the visual network were also significantly widespread in the patient group. The connections of these connector hub regions with cognitive networks were negatively associated (FDR q < 0.05) with cognitive, tremor, and motor function improvement scores. CONCLUSION: In patients with essential tremor, connector hub regions within the cerebellum and thalamus exhibited widespread functional connections with sensorimotor and visual networks, leading to alternative pathways outside the classical tremor axis. Their connections with cognitive networks also affect patients' cognitive function.

Effects of emotional music on visual processes in inferior temporal area.

To investigate the effects of emotional music on visual processes, we analyzed visual evoked magnetic fields (VEF) on listening to emotional music in 14 healthy subjects. Positive and negative pieces of music were delivered during VEF recording following stimulation by emotionally neutral pictures of faces and landscapes. VEF components at 100 (M100) and 150 (M170)ms after stimulus onset were analyzed, and the estimated current strength for M170 following face stimulation was enhanced with negative compared to positive music in the right hemisphere. The equivalent current dipole for M100 and M170 was estimated in the primary visual cortex (V1) and inferior temporal area (IT), respectively. The present results indicate that background music showed a top-down control of the visual processes in IT, which is a core site responsible for the interpretation of facial expression. The emotional contents of music could alter visual processes, especially those involving the face.

Effect of task-irrelevant high-speed verbal stimulation on a visual/verbal word-discrimination task: an event-related potential study.

OBJECTIVES: We investigated whether incomprehensible high-speed auditory speech stimulation was processed and interacted with visual-word discrimination processing. We hypothesised that an interaction might indicate the capacity of working memory (WM) to perform the temporal processing of auditory verbal information. METHODS: We recorded P300 for a visual-word discrimination Oddball paradigm in 14 healthy subjects. Auditory speech and reversed speech stimulation were presented at various speeds as task-irrelevant stimuli during the P300 tasks. RESULTS: The P300 latency was prolonged under forward high-speed speech stimuli (× 2.5 and × 3.5) compared with the standard speed and white noise, but there was no effect of reversed speech stimuli on the P300 latency during the word-discrimination paradigm. CONCLUSIONS: We considered that high-speed speech stimulation was processed without conscious comprehension and competed with verbal processing during the visual-word-discrimination task, possibly by interfering with the use of WM. SIGNIFICANCE: The present study shows the capacity of the brain to process high-speed verbal stimulation and the interaction with a visual-verbal task.

The characteristics of no-go potentials with intraepidermal stimulation.

The objective of this study was to investigate whether no-go potentials during go/no-go tasks were observed after painful stimulation using intraepidermal electrical stimulation. Event-related potentials were recorded by stimulating the medial or lateral side of the left-hand dorsum. Peak amplitudes of N2 and P3 were significantly larger in no-go trials than in go trials at frontocentral electrodes during go/no-go task, but the differences were not found during rest control and choice reaction time tasks. These characteristics of no-go-related potentials were very similar to event-related potential waveforms during visual, auditory, and somatosensory go/no-go tasks. We suggest that cortical activities relating to response inhibitory processing are not dependent on the sensory modality used.

Auditory brain response modified by temporal deviation of language rhythm: an auditory event-related potential study.

The effects of the temporal disruption of language rhythm in Japanese on auditory evoked potentials were investigated in normal subjects. Auditory event-related evoked potentials (AERP) were recorded following syllables using a natural and deviated language rhythm by inserting various (0-400 ms) silent intervals between syllables. The language speed was changed to assess the effect of a deviant rhythm relative to the language speed on AERP in another experiment. The prolonging of intervals did not affect the N100-P150 components until the inserted interval became 400 ms, while the negative component (early negativity, EN), peaking at 250-300 ms, was enhanced when the interval was 100 ms or more. The N100-P150 components following deviated language rhythms did not change during the fast speed but did in the standard and slow speed. We considered that the N100-P150 components were changed by the mixed effects of adaptation and prediction related to the reading speed, and that EN was evoked by deviated language rhythm in a different way from that caused N100-P150 changes, possibly via mismatch detection process between deviant rhythm and intrinsic rehearsed rhythm.

Temporal dynamics of adaptation to natural sounds in the human auditory cortex.

We aimed at testing the cortical representation of complex natural sounds within auditory cortex by conducting 2 human magnetoencephalography experiments. To this end, we employed an adaptation paradigm and presented subjects with pairs of complex stimuli, namely, animal vocalizations and spectrally matched noise. In Experiment 1, we presented stimulus pairs of same or different animal vocalizations and same or different noise. Our results suggest a 2-step process of adaptation effects: first, we observed a general item-unspecific reduction of the N1m peak amplitude at 100 ms, followed by an item-specific amplitude reduction of the P2m component at 200 ms after stimulus onset for both animal vocalizations and noise. Multiple dipole source modeling revealed the right lateral Heschl's gyrus and the bilateral superior temporal gyrus as sites of adaptation. In Experiment 2, we tested for cross-adaptation between animal vocalizations and spectrally matched noise sounds, by presenting pairs of an animal vocalization and its corresponding or a different noise sound. We observed cross-adaptation effects for the P2m component within bilateral superior temporal gyrus. Thus, our results suggest selectivity of the evoked magnetic field at 200 ms after stimulus onset in nonprimary auditory cortex for the spectral fine structure of complex sounds rather than their temporal dynamics.

Variability of P300 in elderly patients with dementia during a single day.

We recorded P300 sequentially during a single day in nine patients with dementia in a health care facility. The variability of the P300 response and the relationship between P300 and the Revised Hasegawa Dementia Scale were investigated. The sequential P300 latency and amplitude measurements varied significantly during the day, but the value changes were not related to the scheduled programs in the facility. Although there was no correlation between the values of latency or amplitude and Revised Hasegawa Dementia Scale (HDS-R), the variability index of the P300 latency correlated with the HDS-R score. Variability in the P300 response was considerable and the reproducibility was poor in elderly patients with dementia during the day, although the P300 latency was consistently prolonged. These results suggested that the variability of P300 was not due to transient changes in the level of consciousness, but was related to the latent pathology of fluctuating cognitive functions in patients with dementia.

Priority of repetitive adaptation to mismatch response following undiscriminable auditory stimulation: a magnetoencephalographic study.

We analysed two different neural mechanisms related to the unconscious processing of auditory stimulation, neural adaptation and mismatch negativity (MMN), using magnetoencephalography in healthy non-musicians. Four kinds of conditioning stimulus (CS): white noise, a 675-Hz pure tone, and complex tones with six (CT6) and seven components (CT7), were used for analysing neural adaptation. The seven spectral components of CT7 were spaced by 1/7 octaves between 500 and 906 Hz on the logarithmic scale. The CT6 components contained the same spectral components as CT7, except for the center frequency, 675 kHz. Subjects could not distinguish CT6 from CT7 in a discrimination test. A test stimulus (TS), a 675-Hz tone, was presented after CS, and the effects of the presence of the same 675-Hz frequency in the CS on the magnetoencephalographic response elicited by TS was evaluated. The P2m component following CT7 was significantly smaller in current strength than that following CT6. The equivalent current dipole for P2m was located approximately 10 mm anterior to the preceding N1m. This result indicated that neural adaptation was taking place in the anterior part of the auditory cortex, even if the sound difference was subthreshold. By contrast, the magnetic counterpart of the MMN was not recorded when CT6 and CT7 were used as standard and deviant stimuli, respectively, being consistent with the discrimination test. In conclusion, neural adaptation is considered to be more sensitive than our consciousness or the MMN, or is caused by an independent mechanism.

Characteristics of processing for trait adjectives in depressive persons: an event-related potential study.

Event-related potentials (ERP) following emotive words were investigated in 22 healthy subjects with high (HD) or low (LD) depressive scores. The ERP was recorded following a visual presentation of emotive adjectives. The adjectives presented included words that subjects felt to be fit or unfit to their own character or traits, and that they perceived as positive or negative. The latency of P300 (P1) for negative words was significantly longer than that for positive words at Pz in HD subjects. The N400 (N1) in HD subjects showed a longer latency than that in LD subjects (p<0.01) at Cz and Pz. However, there was no difference in amplitude between the fit and unfit category, nor in the positive or negative category of words between the LD and HD groups. The present study suggests that an excessive level of cognitive processing in response to passive stimulation by non-specific emotive words occurs in normal subjects with a depressive condition.

Priority of face perception during subliminal stimulation using a new color-opponent flicker stimulation.

We developed a new method of color-opponent flicker (COF) stimulation, and investigated behavioral responses for object discrimination at the around threshold frequency of COF stimulation. Pairs of figures, a face, flower, the letter "G" and a random pattern, were drawn with a red and green checkerboard with a black mesh. COF stimulation was produced by presenting pairs of figures alternately (red-green-red-green-) at various frequencies (30-120 Hz). A discrimination task for objects during COF stimulation was performed by 16 healthy subjects. Threshold frequency of COF stimulation was between 50 and 75 Hz. The accuracy rate for face discrimination was significantly higher than those for other objects (p<0.01, ANOVA with Fisher's PLSD multiple comparisons test). The present COF stimulation technique could be useful to investigate subliminal processes of the visual system, and the present results indicate a higher sensitivity and selectivity for face discrimination than those for other objects.

Differential priming effects of color-opponent subliminal stimulation on visual magnetic responses.

We investigated the effects of subliminal stimulation on visible stimulation to demonstrate the priority of facial discrimination processing, using a unique, indiscernible, color-opponent subliminal (COS) stimulation. We recorded event-related magnetic cortical fields (ERF) by magnetoencephalography (MEG) after the presentation of a face or flower stimulus with COS conditioning using a face, flower, random pattern, and blank. The COS stimulation enhanced the response to visible stimulation when the figure in the COS stimulation was identical to the target visible stimulus, but more so for the face than for the flower stimulus. The ERF component modulated by the COS stimulation was estimated to be located in the ventral temporal cortex. We speculated that the enhancement was caused by an interaction of the responses after subthreshold stimulation by the COS stimulation and the suprathreshold stimulation after target stimulation, such as in the processing for categorization or discrimination. We also speculated that the face was processed with priority at the level of the ventral temporal cortex during visual processing outside of consciousness.

Cortical activities relating to modulation of sound frequency: how to vocalize?

This is the first report to clarify the underlying mechanisms of processing in the modulation of frequencies (tones) in humans using magnetoencephalography (MEG). Volunteers were instructed to vocalize a simple vowel sound (/u/) after receiving a cue (S2) for either one of three (low, middle, or high fundamental frequencies) (F0s). Three tasks, (1) the modulated vocalization task in which the subjects were asked to modulate vocalization tones according to S2, (2) the non-modulated vocalization task in which the subjects were asked to vocalize the same sound (/u/) with a fixed F0, and (3) the image task in which the subjects had to modulate according to S2 and imagine the vowel (/u/) sound, but not vocalize it. In all tasks, two clear components, 1M and 2M, were recorded at approximately 190 and 290 ms after the S2. Since both were identified even in the Image task, they appear to be specifically related to activity for modulation. The equivalent current dipoles of both 1M and 2M were estimated to lie mainly in the inferior frontal lobe or insula in both hemispheres. Therefore, the activity relating to modulation mainly took place in the inferior frontal lobe or insula in both hemispheres starting about 200 ms after the viewing of a cue.